How to properly merge multiple collections in Laravel

I want to merge multiple collections into one. I do have a solution, which is the following:

$allItems = $collection1->merge($collection2)
                        ->merge($collection3)
                        ->merge($collection4)
                        ->merge($collection5);

This actually does work, but I run into problems in cases where some or all of the collections contain no objects. I get an error along the lines of call to merge() on non object.

I actually tried to create an array of all of the collections, and then iterate through them, while checking their validity, but it didn't work and I feel it wasn't very elegant.

How can I elegantly iterate through this process of merging multiple collections, while taking into account that some or all of the collections might be empty or invalid? Appreciated!

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